Photoremovable caging groups find extensive use across many fields ranging from cell biology to materials science. The general requirement of UV or blue light is a significant limitation due to associated toxicity and poor tissue penetration. By contrast, light between 650 and 900 nm, often referred to as the near-IR window, is cytocompatible and has significant tissue penetration (centimeters). Generally useful single photon reactions in the near-IR range would allow uncaging approaches to be applied in complex biological settings. My lab is approaching this difficult challenge by defining and then using the chemical reactions involved in the photodecomposition or photobleaching of near-IR fluorophores. These oft-encountered light-initiated processes can occur with rapid kinetics, often undesirably so. Our lab has pioneered the notion that these reactions can be used in a rational and deliberate fashion for in vivo drug delivery. This approach has led to the first small molecule photocages that can be activated by 780 nm with in vivo efficacy. Our current efforts in this area are split in two aims. Aim 1: Development and mechanistic studies of near-IR photorelease chemistry. We have developed an uncaging reaction sequence initiated by near-IR light using readily synthesized C4'-dialkylamine-substituted heptamethine cyanines. We have shown that a variety of phenol- and amine- containing small molecules are quickly uncaged upon irradiation with low energy light. Detailed mechanistic studies involving mass spectrometry, NMR, and absorbance techniques have shown that release occurs through regioselective C-C cleavage and then hydrolysis of the C4'-amine. We are currently broadening the scope of the release process and examining aspects of the mechanism in detail using computational (collaboration with Dr. Joseph Ivanic) and experimental techniques. As part of this effort, we have developed an approach that enables the control release of amine payload through an approach that involves cyanine photooxidation followed by beta-elimination. Aim 2: Application of uncaging reactions for targeted drug delivery. Existing methods that use light for therapeutic interventions typically rely on the local generation of reactive oxygen species (ROS). The local delivery of potent therapeutic agents elicit alternative mechanistic paradigms, while achieving otherwise unattainable potency. We are applying our light-cleavable chemistry for targeted drug delivery (collaboration with Dr. Hisataka Kobayashi). This approach merges the unique potency of small molecule drugs with the high spatial control afforded by light release and molecular targeting. The use of tissue penetrant, cytocompatible near-IR light is critical because existing uncaging chemistries using UV or blue light would not be suitable for this application. In this area, we reported the first example of near-IR light cleavable antibody drug conjugate strategy. We have developed conjugates that release the potent anticancer natural product, duocarmycin. These conjugates can be tracked in vivo using fluorescence and uncaged attainable flux from an external CW laser source. These compounds have shown highly promising antitumor activity in in vivo models. We are currently pursuing additional optimization efforts, including the application of distinct targeting mechanisms.